1. Field of the Invention
The present invention relates to a driving force transmission mechanism that can prevent a follower wheel from rotating together with a driving wheel in a play section, and a damper apparatus that can drive two open-close plates independently from each other through the driving force transmission mechanism.
2. Related Background Art
A variety of driving force transmission mechanisms that transmit driving force from a driving wheel (or gear) to a follower wheel (or gear) are known. One of such driving force transmission mechanisms engages a driving wheel with a follower wheel to make the follower wheel to follow rotations of the driving wheel in a linked movement section, and releases the engagement between the driving wheel and the follower wheel to rotate only the driving wheel in a play section. This driving force transmission mechanism may be assembled in a damper apparatus of a refrigerator, for example, to drive two open-close plates independently from each other with one driving source, to supply cold gas from an evaporator to different chambers within the refrigerator.
FIGS. 8(a) and 8(b) shows a conventional driving force transmission mechanism. As shown in FIG. 8(a), the driving force transmission mechanism includes a single driving motor 106 that is capable of normal and reverse rotations, a reduction gear train 107 composed of four gears for reducing the rotation of a pinion 106a that is mounted on a rotary shaft of the driving motor 106, a first driving gear 108 to which the rotation of the driving motor 106 that is reduced by the reduction gear train 107 is transmitted, and a first follower gear 109 that engages the first driving gear 108 only in a specific section. The first follower gear 109 is linked to a rotary shaft 104a of a first open-close plate among two open-close plates. Therefore, when the first driving gear 108 engages the first follower gear 109 and rotates in a normal direction or a reverse direction, the first open/close plate opens or closes.
Further, as shown in FIG. 8(b), a second driving gear 110 is disposed concentrically with the first driving gear 108 at a position where the second driving gear 110 overlaps the first driving gear 108, and the second driving gear 110 engages a second follower gear 111. The second follower gear 111 is linked to a rotary shaft 105a of a second open/close plate among the two open/close plates. Therefore, when the second driving gear 110 engages the second follower gear 111 and rotates in a normal direction or a reverse direction, the second open/close plate opens or closes.
Because the two open-close plates are independently driven by the single driving motor 106 as a common driving source, the damper apparatus operates in a manner that, in a linked movement section among a rotation section of the first driving gear 108, the first driving gear 108 and the second driving gear 110 are engaged with each other such that the second driving gear 110 follows the rotation of the first driving gear 108; and in a play section, the engagement between the first driving gear 108 and the second driving gear 110 is released so that only the first driving gear 108 rotates.
However, with this mechanism, when the first driving gear 108 rotates in the play section, its driving force is transmitted to the second driving gear 110 through grease or the like that is present between the first driving gear 108 and the second driving gear 110, and in some cases, the second driving gear 110 rotates together with the first driving gear 108.
In the damper apparatus shown in FIG. 8(b), groove sections 110c and 110d are formed along an outer circumferential portion of the second driving gear 110, and a leaf spring 112 with an engagement section 112a is provided. The engagement section 112a enters the groove section 110c or 110d during the play section to stop the rotation of the second driving gear 110, which prevents the second driving gear 110 from rotating together with the first driving gear 108.
However, the click-type following rotation preventing mechanism such as the one described above in which the engaging section 112a of the leaf spring 112 enters the grooves 110c and 110d has a problem in that a substantially large force is required for the engagement section 112a of the leaf spring 112 to ride over the stops formed by the groove sections 110c and 110d. 
FIGS. 9(a) and 9(b) show other following rotation preventing mechanisms in which a leaf spring 112 is provided to abut against an arcuate portion of the second driving gear 110. In these following rotation preventing mechanisms, only frictional force between the leaf spring 112 and the second driving gear 110 is used to prevent the rotation of the second driving gear 110. Under normal conditions, these following rotation preventing mechanisms may not have any particular problem. However, for example, when the grease deteriorates and its viscosity increases, following rotations of the second driving gear 110 cannot be securely prevented. On the other hand, if a large pressure force is set to the leaf spring 112 to securely prevent following rotations of the second driving gear 110 in the mechanism shown in FIG. 9(a) or FIG. 9(b), a substantially large force is required during the linked movement section where the second driving gear 110 is also driven to rotate, and abrasion occurs rapidly on the leaf spring 112 or the outer circumferential surface of the second driving gear 110.